1. Field of the Invention
The present invention relates to a method for manufacturing a battery, and more particularly, to a method for connecting the end faces of electrode plates with a collector plate.
2. Description of Related Art
For a rechargeable battery structure, a prismatic structure comprising layered positive electrode plates, negative electrode plates and separators has been used principally with aqueous solution-type rechargeable batteries. Such structure serves to increase the electrode surface area as much as possible within a restricted space, and in addition to raising the reactive efficiency of the electrode plates, thereby enabling a large current to be drawn. It therefore significantly affects battery characteristics.
In relation to rechargeable batteries having a structure comprising a layered plurality of electrode plates, various proposals have been made regarding mechanisms for extracting current from the respective electrode plates. One such proposal relates to a structure wherein lead-shaped conductors are attached to or derived from each individual electrode plate, gathered together, and then bonded to an electrode pole which extracts current to the exterior of the battery case.
However, in such structure as described above, the lead-shaped conductor sections occupy a large volume, and hence present a significant restriction when seeking to reduce the overall size of the battery.
Therefore, as illustrated in FIG. 8, a method has been devised wherein end faces of respective electrode plates 1a, 2a that are layered upon one another are welded directly to a collector plate 4. According to this method, electrode groups 1 and 2 constituted respectively by pluralities of positive electrodes 1a and negative electrodes 2a are respectively butted against and bonded to the surface of a collector plate 4, in a perpendicular attitude to same, a T-shaped joint being formed between each collector plate 4 and electrode group 1 or 2.
For this bonding operation, it is possible to apply an arc welding method as disclosed in Japanese Patent Publication No. 61-8539, an electron beam welding method as disclosed in Japanese Patent No. 2616197, or the like. However, if a welding method of this kind is used for bonding groups of electrode plates with collector plates in a battery as illustrated in FIG. 8, since the distance between the respective electrode plates 1a, 2a is set to an extremely small distance in order to reduce the size of the battery, heat will be transmitted to the separators 3 provided between the respective electrode plates 1a, 2a, causing same to melt and readily provoking shorting between the positive electrode plates 1a and negative electrode plates 2a, and hence it is difficult to join the aforementioned elements in a suitable manner.
The present invention was devised in view of the foregoing problems associated with the prior art, an object thereof being to provide a method for manufacturing a battery adopting a bonding joint structure between electrode plate groups and collector plates which enables the volumetric efficiency of the battery to be increased, wherein bonding is performed in a suitable and reliable manner.
The method for bonding collector plates to end faces of electrode plates according to the present invention comprises the steps of:
providing a solder material made from nickel alloy on a surface of a collector plate; and
arranging a plurality of electrode plates perpendicular to the collector plate so that end faces of the electrode plates abut with the solder material on the collector plate;
irradiating an electron beam onto the collector plate from a direction opposite from the electrode plates for causing the solder material to melt, thereby bonding the end faces of the electrode plates with the collector plate.
By interposing a solder material having a lower melting point than the materials composing the electrode groups and collector plates in the joint between same, it is possible to join electrode plates to a collector plate by causing the solder material to melt by irradiating an electron beam onto the collector plate. The amount of heat applied to the joint can be reduced compared to a method where the respective elements are bonded directly by welding, and hence the electrode plates and collector plate can be bonded in a reliable manner, without imparting any thermal effects on regions other than the joint, such as the separators.
Desirably, the nickel alloy used for the aforementioned solder material is a binary alloy of nickel and phosphorous.
If the electron beam is irradiated onto a plurality of positions on the collector plate, then the collector plate and electrode plates can be bonded together more reliably, and it is also possible to maintain high collector efficiency. Furthermore, by ensuring that adjacent irradiation positions are not irradiated consecutively, in a portion of or all of the irradiation positions, a region irradiated by the electron beam will have cooled sufficiently before the electron beam is irradiated onto an irradiation position adjacent thereto, and hence thermal effects can be reduced in a more reliable manner.
The amount of irradiation of the electron beam is changed with respect to the lateral direction of the collector plate. Since dispersion of heat is particularly high at the ends of the collector plate, a uniform overall join state is obtained by increasing the amount of irradiation in the end regions. Specifically, for instance, the electron beam should be irradiated in a consecutive fashion in the lateral direction of the collector plate, whereupon the electron beam is irradiated further onto either end portion thereof.
If the electron beam is first irradiated onto a beam collector and the output thereof is stabilized, before it is irradiated onto the joint between an electrode plate and a: collector plate, then a highly reliable bonding can be accomplished.
Furthermore, by irradiating the electron beam onto the same position a plurality of times, it is possible to ensure sufficient input heat, even when using a compact and inexpensive electron beam irradiation device having a small per-operation irradiation energy.
Other and further objects, features and advantages of the invention will be apparent more fully from the following description.